So for me it is looking like there is one ethereum adress handling all the ERC-20 token desposits.

I followed just one deposit of mine to find out about that.

https://etherscan.io/address/0x6871eacd33fbcfe585009ab64f0795d7152dc5a0#tokentxns

I think the transfer is working that way my wave account is linked via my specific ethereum token desposit address.

When I perform a desposit that one is via smart contract directly transfered to the above "handle address" which if confirmed there gives me the balance on my waves account.

Nevertheless I'am not a expert in that and I do not really see any hints on that adress how the interessts are created. Perhaps anyone else can skip in here for me.